Four broad groups of experiments are proposed in this research which vary widely in methodology but are all concerned with cognitive processing during the production and perception of language. The first two groups examine sentence processing in terms of performance structures shared by speaker and listener (a paradigmatic perspective) and on-line processing of sentences (a syntagmatic perspective) in speech and sign -- contrastively. Dependent variables include recall accuracy and latency, pause distributions, intelligibility, shadowing lag, and restoration errors. The remaining two groups of experiments are focused at the lexical and morphological levels of sigh language. They examine the perception and production of movement in sign formation and inflection -- a major aspect of the phonological code, and the pictorial bases of sign -- the major opposing force to encodedness. Dependent variables include identification and discrimination accuracy and latency within the framework of signal detection theory; movement, handshape and location changes under delayed recall, serial transmission, diachronic change, repetition and speeding in discourse; and various measures interpreted as reflecting analog mental representations during sign processing.